Effect Pesticides have on Frogs
Atrazine, one of the most widely used pesticides in the world, wreaking havoc with the sex lives of adult male frogs, three quarters maul them and becoming one of 10 women, according to a new study from the University of California, Berkeley biologists.
The 75 percent that are chemically castrated are essentially “dead” due to their inability to reproduce in the wild, reports UC Berkeley Tyrone B. Hayes, professor of integrative biology.
“These men frogs lack of testosterone and all that testosterone controls, including sperm. Thus fertility is as low as 10 percent in some cases, and that’s only if isolating animals and linked with the women, “he said. “In an environment where they are competing with exposed animals have zero chance of reproduction.”
The 10 percent or more, which in turn of men in women – something not known to occur under natural conditions of amphibians – can successfully mate with the male frogs, but because they are genetically male, all his children are men.
“When these kids grow, depending on the family, we will reach any part of the females 10 to 50 percent,” said Hayes. “In a population, females genetically male may reduce or eliminate a population just because they skew the sex ratio so bad.”
Although the experiments were conducted in a common laboratory frog, the African clawed frog (Xenopus laevis), field studies indicate that atrazine, a potent endocrine disruptor, in the same way it affects the frogs in the wild and possibly could be one of the causes of amphibian declines around the world, “Hayes said.
Hayes and his colleagues at the University of California at Berkeley, report their findings in the earlier editions of this week’s online Proceedings of the National Academy of Sciences. Last week, Hayes and colleagues published a study of the effects of pesticides on amphibians in the Journal of Experimental Biology and concluded that atrazine is a contributor to amphibian declines worldwide.
“This kind of problems, such as sex-reversed animals skew the sex ratio are much more dangerous than any chemical that could kill a population of frogs,” he said. “In exposed populations, there seems to be breeding frogs, but in fact, the population breaks down very slowly through the introduction of these altered animals.
Some 80 million pounds of the herbicide atrazine are applied annually in the United States in maize and sorghum for controlling weeds and increased crop yields, but their widespread use and also makes the pesticide atrazine the most common contaminant of water groundwater and surface water, according to various studies.
More and more research, however, is showing that atrazine interferes with the endocrine hormones, like estrogen and testosterone – in fish, amphibians, birds, reptiles, rodents and even laboratory human cell lines at levels of parts per billion. Recent studies have also found a possible link between birth defects and low birth weight and exposure to atrazine in utero.
As a result of these studies, the Environmental Protection Agency (EPA) is revising its rules for the use of pesticides. Several states are considering a ban on atrazine, and six class action lawsuits have been filed seeking to eliminate its use. The European Union already bans the use of atrazine.
Hayes studies in the 2000s were the first to demonstrate that the hormonal effects of atrazine disrupt sexual development in amphibians. Working with the African clawed frog, Hayes and his colleagues showed in 2002 that hermaphrodites are reared tadpoles in water contaminated with atrazine – which develop both female (ovaries) and males (testes) gonads. This occurred at atrazine levels as low as 0.1 parts per billion (ppb), 30 times lower than levels allowed in drinking water by EPA (3 ppb).
Later studies showed that native leopard frogs (Rana pipiens) collected from atrazine-contaminated streams in the central region, including areas up to 1,000 miles from where atrazine is applied, often had eggs in their testes. And many men had lower testosterone levels than normal women and smaller than normal voice boxes, likely limiting their ability to call their peers.
Hayes’s research also many frogs in Midwestern streams polluted by pesticides atrazine and other compromised immune systems, leading to increased mortality from bacterial diseases.
Early studies were hampered by the inability to easily distinguish genetically genetically male from female frogs. The male frogs have two identical sex chromosomes (ZZ), while women have both a Z and a W – unlike human males and XX female XY. But because all chromosomes of a frog the same appearance under a light microscope, it is not easy to distinguish males from females.
To overcome this, Mr Hayes, Roger Liu developed a line of all male frogs for genetics would be unambiguous.
“Before we knew it has fewer men than we should have, and we hermaphrodites. Now we have clearly demonstrated that many of these animals are sex reversed in men,” Hayes said. “We have animals who are women, meaning that they behave like women: they have estrogen, lay eggs, mate with other males. Atrazine caused a hormonal imbalance that has made them into the wrong sex, in terms of its genetic constitution. ”
Coincidentally, another lab in 2008 discovered a sex-linked genetic marker in Xenopus, which has enabled Hayes to confirm the genetic sex of the frogs.
Hayes’s study, where 40 frogs lived for almost three years after hatching in water with 2.5 ppb atrazine, 10 per cent of frogs appeared to be resistant to the effects of the pesticide. In ongoing studies, Hayes is investigating whether this apparent resistance is inherited, and whether the sex workers, men have invested more susceptible children.
Syngenta, which manufactures atrazine, disputes many of these studies, including Hayes, showing the adverse effects of presticide. However, Hayes said that “when you have worldwide studies showing problems with atrazine in all vertebrates that has been regarded – fish, frogs, reptiles, birds, mammals – all of them can not be wrong”.
“What people have to realize is that, as with pharmaceuticals to take, they must decide whether the benefits outweigh the costs,” he said. “Not all amphibians and all human beings affected by atrazine, but do not want to take a chance with all the other things we know that atrazine does not, not only humans, but the rodents, frogs and fishes? ”
Long-term studies of Hayes of the effects of atrazine on frogs have received help from many undergraduates at UC Berkeley, including co-authors on the current document: Vicky Khoury, Anne Narayan, Mariam Nazir, Andrew Park, Lillian Adame Elton Chan, and graduate students Travis Brown, Daniel Buchholz, Sherrie and Theresa Gallipeau Stueve.
The work was funded by the company’s Water Park, Mitch Kapor, Freada Klein, Mitch Kapor Foundation, the David, the Cornell-Douglas, Wallace Foundation, the class of 43 at UC Berkeley and Professor of Biology Howard Hughes Fellows Program.
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